The PCA9534 consists of one 8-bit Configuration (input or output selection), Input Port,
Output Port, and Polarity Inversion (active high or active low) register. At power on, the I/Os are
configured as inputs. However, the system master can enable the I/Os as either inputs or outputs by
writing to the I/O configuration bits. The data for each input or output is kept in the
corresponding Input or Output register. The polarity of the Input Port register can be inverted
with the Polarity Inversion register. All registers can be read by the system master.

The system master can reset the PCA9534 in the event of a timeout or other improper
operation by utilizing the power-on reset feature, which puts the registers in their default state
and initializes the I2C/SMBus state machine.

The PCA9534 open-drain interrupt (INT) output is activated when
any input state differs from its corresponding input port register state and is used to indicate to
the system master that an input state has changed.

INT can be connected to the interrupt input of a microcontroller.
By sending an interrupt signal on this line, the remote I/O can inform the microcontroller if there
is incoming data on its ports without having to communicate via the I2C
bus. Thus, the PCA9534 can remain a simple slave device.

The device's outputs (latched) have high-current drive capability for directly driving
LEDs. It has low current consumption.

Three hardware pins (A0, A1, and A2) are used to program and vary the fixed
I2C address and allow up to eight devices to share the same
I2C bus or SMBus.

The PCA9534 is pin-to-pin and I2C address compatible with the
PCF8574. However, software changes are required due to the enhancements in the PCA9534 over the
PCF8574.

The PCA9534 is a low-power version of the PCA9554. The only difference between the
PCA9534 and PCA9554 is that the PCA9534 eliminates an internal I/O pullup resistor, which
dramatically reduces power consumption in the standby mode when the I/Os are held low.

The PCA9534A and PCA9534 are identical, except for their fixed
I2C address. This allows for up to 16 of these devices (8 of each) on
the same I2C bus.